1. Field of the Invention
The present invention relates to the identification of a programmable logic device (PLD), and specifically to a system and a method for using a PLD identification code.
2. Description of the Related Art
Identifying integrated circuits (ICs) is known in the art. Providing a unique identification (ID) for each IC can be useful in determining the functionality or performance of the IC, monitoring inventory, and allowing law enforcement to quickly find and recover stolen ICs. A typical IC identification scheme includes providing a bit pattern that is unique to a specific IC.
In one embodiment, each IC can have its own silicon ID. For example, in a proprietary scheme licensed by SiidTech Inc., an array comprising pairs of transistors (typically located on the periphery of the IC) provides the unique IC identification, wherein each pair of transistors provides one bit of the ID. In this scheme, an ID checker (typically located adjacent the array) senses the difference in the threshold voltages of each pair of transistors and assigns a logic value to each pair of transistors based on the difference in the threshold voltages. Thus, the SiidTech ID scheme advantageously relies on the inherent statistical variation in the transistors to provide the silicon ID. In one implementation, the array includes 310 transistors, thereby providing 155 bits in the silicon ID.
Unfortunately, the threshold voltage of a transistor can change, albeit rarely, due to temperature and voltage. In fact, SiidTech indicates that in an array providing 155 bits, as many as nine bits can change over the lifetime of the IC. However, when an IC is being identified, even a single bit changing will result in an incorrect identification. Therefore, a need arises for a system and method for providing a unique silicon ID that ensures a correct identification.